Pneumatic stapler



Jan. 7, 1958 H. N. FAccou 2, 0

. PNEUMATIC STAPLER Filed Sept. 25, 1952 3 Sheets-Sheet 1 .IZTVE T2 ZET Harlan F RCCOLL Jan. 7, 1958 H. N. FACCOU PNEUMATIC STAPLER Filed Sept. 25, 1952 a 3 Sheets-Sheet 2 N g 5| ITWE 7727:? Y 4 Harlan]? FZzcaou Jan. 7, 1958 H. N. FACCOU PNEUMATIC STAPLER 3 Sheets-Sheet 3 Filed Sept. 25. 1952 HarlazzF Fi'zccozz III/III m rmm United States Patent PNEUMATIC ST APLER Harlan-N; Faccou, Santa Ana, Calif.

Application September 25, 1952, Serial'No. 311,481

6-Clai'ms.- {CL 1-'-44.4)

The present invention relates to improvements in machines for driving fastening devices such as staples, and more particularly concerns pneumatically operated stapling machines.

An objectionable operating characteristic of most prior pneumatically operated devices for driving-fasteners such as staples, pins, nails, or the like, has resided in pro nounced jarring or hopping due to the recoil action incident to the increasing velocity of the mass of reciprocating elements, such as piston and driving bladeor plunger and the instantaneous endingiof this mass movement. In such adevice ithas beenacgeneral practice to rely upon the weight ofthe reciprocating mass, similarly as with the head of a hammer, in order-to have-suflicientdriving force to drive the fastenersinto -the desiredmedium. Full driving pressure .is attained progressively from :the start of the drivingstroke of the pistonto the conclusion of the -drivingi.stroke,- with-a noticeable kick back reaction when not only is thermaximum driving pressure attained but .the-reciprocating-mass "is w also-necessarily brought to an abrupt halt at theend'of its driving stroke;

It .is accordingly an important object of the present inventionto provide a pneumatically operated fastener driving device substantially free from recoil :in the driving stroke but operative smoothly and-,powerfully-indriving or setting the fasteners.

Another object of the invention is to provide novel means for assuring maximum driving .power in a fastener driving device for smooth substantially recoile'ssoperation.

A further object ofthe invention is' to provide' 'nove'l pneumatically operated sear mechanism for improving the action of pneumaticallyoperated stapling or like machines.

Still: another object-of-ttheinventionris to provide novel staple drive mechanism for pneumatic staplers.

Still another object of the invention istoprovide an improved pneumatic stapler which is especially suitable for portable f operation:

Other objects, features and advantages of the present invention will be readily apparent from the following detailedtdes'c'ription of certain preferred embodiments thereof taken in conjunction with the accompanying drawings in which:-

Figure 1 is asideelevational view of a pneumatic stapler embodying features of the invention;

Figure 2- is a to'p plan-view of the stapler;

Figure'3 is an enlarged-meteor less conventionalized longitudinal vertical sectional view through' the' stapler taken substantially along'theline l'lIIII ofFigureZ;

Figure '4 isa frontelev'ational view of the stapler;

Figure "5 is a horizontal sectional detail view taken substantially on the line "V-V of Figure 3;

Figure 6*is a fragmentary sectional detailviewtaken substantially along the-lineVI VI' of Figure 3;

Figure "7 is a fragmentaryse'ctional detail view taken substantially alongthe'lin'e VII-VII of Figure 3; and

2,818,570 Patented Jan. 7, 1958 Figure 8 is a fragmentary longitudinal vertical sectional view through a modified construction embodying the invention.

A pneumatically operated fastenerdriving machine 10 embodying the featurespfflthe invention, Figures l-4, is in the form ofa; readily portable stapler, although it will be apparent that various features ofthe invention may be readily adapted to stationary bench or stand mounted types of-pneumaticfastener driving or setting machines. The machine 1'0-com'prises'a' body 11 which, as shown may be acne-piece moldedor cast structure. The material from-whichthe body 11' is made is preferably of as lightweight;consistentwithadequate strength for the service requirements: of the machine, as practicable. For this purpose, :themateria'l may be a lightweight metal= or alloy or a hardenably' molda-ble plastic material;

In the present instance, the-body 1'-1 of the machine is constructe'cl for'balanced-portable manipulation and is of elongated'substantially'fflattened form, provided substantially centrally with a -:han'd clearance holeoropening 12. This opening is defined by an upper longitudinally extendinghandle portion 3,-a lower-' b'ase' portion 14, a rear magazine portion or section 1'5,an"d a front driving head portion- 13. The-construction and arrangement of the body 11 is thus' of-substantially balanced type from a standpoint of weight distribution to facilitate handling in service.

In the exemplary embodiment of the machine 10' as shownit is ad'apted ferforniing, severing and'driving successive staples IS KFigUreS)"from-a continuous staple blank strip 19; l'nsuch strip 'a-con'tinuous series of flat sheet'metal staple blan'ks is supplied from arch of substantial size o'ffrotn 1500' to "2000 blankshoused-within the magazine section lb'of the machine and fed from the lower portionof the magazine chamber-down a' ramp 20 forwardly under the base portion -1'4 of the machine between a paii' o'f downwardl'yqprojecting curb flanges 21 on abottom-plate 22'; thefor'wardend of the .machine the strip 19 travels over an anvil member orblock 23 suitablysupported-atthe l owe'r portion of the head section 17- ofthe"machine""immediately behind a staple driveway 24: In the presentins'tance the'driveway 24 is provided with a dovt'rnw'a'r'd. extension '25 of the type adapted for engaging and'holding the margins of upholstery material to be stapled to the framework of a piece of furniture. The extension 25 comprises in part a nose piece271which may beinthe'forr'n of a removable gatelocked inplacebymeans of aslidinglatch 28 having a snap interlock 29with the front of the gate 27 and disengagea'ble by'upward movement to release the gate member27'feriemeva1 to open" the staple guideway 24 and expose the fi'ont of the anvil-'23. In addition to the retaining cooperation therewithof the slidable latch member '28, the gate member'27 may be retained against lateral displacementlin serviceby suitable means such as pins or the like,.as indicated in dashoutline in Figs. 1 and'3 adjacent tothetopof the gatezmember and cooperatively extending, into the contiguous portion of the body of the machine.

Forming, cutoff andldrivingcof the staples 18 is accomplished byforming. and driving mechanism 30 which is pneumatically drivenzofI as light weight construction as practicable. To-this end,-.adriving plunger3-1 is equipped with a yokeformerl'iiand'adriverblade 33. Both the former 32 and the driver blade 33- are simultaneously driven-with the driving. end sof the driver V3?; in advance of the former'32 so that the staple 18 at the'leading end of the staple strip is severedfrom the' stripby' cooperation of thedlivingbla'de' with the'fron't end of the anvil 23 and then driven onward in the guideway'M toward the 3 exit at the tip of the extension 25, and the former 32 then cooperates with a forward forming section 34 on the anvil to bend the oppositely extending legs of the next succeeding staple blank in the strip into the U-shaped staple form.

The stem or plunger member 31 has at the end opposite to the driver a piston 35 operable reciprocably in a cylinder 37. The cylinder member 37 is preferably formed as a generally elongated cup-shaped machined member secured within a vertical bore 38 in the head section 17 of the machine above the guideway 24. At its lower end the cylinder 37 is held in place by a retaining ring 39 at the bottom, and a nut 40 externally threaded at its top end bears against the top of the head portion 17 of the machine body. The cylinder is held against turning by means such as a set screw 41 extending into a short longitudinal slot near the bottom of the cylinder.

At its upper, open month end, the cylinder 37 is closed by a screw cap 43 held against unintentional turning loose by a turn-preventing retainer 44 thereon having a dog flange 45 interlockingly engaging within a peripheral notch 47 on the retainer nut 40 and its outer edge bent upward and against a flat on the screw cap 43. The cap 43 has a central depending stop boss 48 engageable with the piston 35 in the upper limit of movement of the piston and main taining an air space between the cap 43 and the top of the piston.

In its fully retracted position into which it is normally urged by a return spring 49, the piston 35 abuts against the stop boss 48. Limit upon the range of downward movement in the driving stroke of the piston 35 is defined by engagement of the lower edge of a skirt flange St on the piston against a bumper 51 supported in the blind end of the cylinder 37. This bumper 51 may comprises a rubber or rubber-like annulus supported between the lower portion of the cylindrical internal wall of the cylinder and a metal internal retainer ring 52 which confines the elastic, resilient bumper ring 51 against spreading radially inwardly and thus interfering with the lower end portion of the coiled compression return spring 49 which rests against the blind end or bottom of the cylinder concentrically about the stem 31. At its upper end the spring 49 thrusts against a head flange 53 at the upper end of the stem 31 concentrically within the inverted cup of the piston 35.

Pneumatic power for operating the staple forming and driving mechanism 36 in a single shot operation is afforded by a valve controlled system. To this end, compressed air under appropriate pressure is applied to a header passage 54 which is conveniently provided as a longitudinal bore in the upper portion of the handle 13 of the machine. For the convenience of the user, provision is made for attachment of either the rear end or the forward end of the header 54 with a compressed air source, and for this purpose the header is provided with an internally threaded rear inlet 55 and an internally threaded forward and preferably upwardly directed inlet 57. By way of example, the forward inlet 57 is illustrated as closed by a screw plug 58 while the rear inlet 55 has a nipple 59 threaded thereinto for connecting a compressed air source such as a compressor or compressed air tank (not shown).

From the supply header 54, compressed air is adapted to be selectively released into a reservoir or supply passage 61 by way of a port 62 under the control of a normally closed valve 63. By preference the valve 63 is located adjacent to the forward end of the handle portion 13 of the machine body. A downward continuation of the port 62, comprising a bore 64 opens into the hand hole 12 to accommodate a bushing 65 providing a bearing for a downwardly projecting operating stem 67 on the valve 63 which normally protrudes a substantial distance below the outer end of the bushing. A trigger lever 68 pivotally mounted by means of a pin 69 on the machine body adjacent the forward upper portion of the hand hole 12 underlies the plunger stem 67 and is engageable with the outer end of the stern. Through this arrangement a user 4 handling the machine by manually gripping the handle portion 13 can conveniently manipulate the trigger 68 with his forefinger.

When the trigger 68 is squeezed upwardly, it moves the valve stem 67 upwardly and unseats the valve 63 from a valve seat 7 it at the mouth of the port 62. Such unseating movement is resisted by a biasing spring 71 in the form of a coil compression spring thrusting against the top of the valve 63 and having its upper end seated within a socket 72 counterbored in the inner end of a closure plug 7'3 threaded into an access opening concentrically disposed above the port 62.

Air under pressure admitted to the'delivery passage 61 is conducted thereby to a port 74 in the cylinder 37 opening into the space between the top of the piston 35 and the closure cap 43. This would normally drive the piston 35 in opposition to the biasing spring 49 to motivate the former 32 and the driver 33 in a working stroke.

However, according to the present invention, in order to assure that full driving pressure is developed on the head of the piston 35 before starting of the driving stroke, pneumatically operated means are provided for delaying operation of the piston until the proper pressure has accumulated in the cylinder 37 over the piston. For this purpose, a sear arm 75 normally engages retainingly with the driving mechanism 30 to hold the latter inactive. In a convenient arrangement, the sear arm 75 extends forwardly from within a chamber 77 in the lower portion of the head section 17 of the machine body through an opening 78 into the upper portion of the guideway 24 and has an oblique engagement shoulder 79 engaging with a complementary oblique shoulder 80 within the bight of the yoke of the former 32. The sear arm 75 is part of and projects forwardly from an above center portion of a depending, vertically elongated lever 81 rockably pivoted upon a pin or rock shaft 81a extending across the upper end portion of the chamber 77. By virtue of such pivoting of the lever 81, swinging movement of the lever rearwardly swings the sear arm on an arc downwardly and rearwardly away from the shoulder 79 so that the sear releases from the shoulder without any component of back thrust on the shoulder incident to the release which might interfer with free movement of the driver after release or impose any strain upon the mechanism.

Normally the lever 81 is biased forwardly to hold the sear projection or arm 75 in the inactivating or retain ing relation to the forming and driving mechanism 30. For this purpose, the lower end portion of the lever 81 is pivotally connected as by means of a pin 82 to a link structure 83 which projects rearwardly and is pivotally connected as by means of a pin 84 to a piston rod or stem 85 extending rearwardly and having at its rear end portion a piston 87. A biasing spring 88 of preferably the coiled compression variety thrusts forwardly at one end against the head of the piston and at its rear end bears against a backing or thrust plate 89 at the rear end of a bore 90 lined with a hardened cylinder 91 within which the piston 37 is reciprocable. The biasing spring 88 is selected for predetermined thrust force. As a result of this arrangement, the forming and driving mechanism 30 cannot operate in a driving stroke but is held inactive by the sear 75 until a counterforce is developed which will overcome the thrust of the spring 88 upon the piston-link-lever system of which the sear is a part.

For pneumatically retracting the piston 87 in opposition to the bias of the spring 88, a restricted branch duct 92 leads from the supply passage 61 downstream from the entry port 62 and communicates through a port 93 in the forward portion of the cylinder sleeve 91 in front of the piston 87. A centrally bored closure plug 94 seals the mouth of the forward end portion of the cylinder 91 in spaced relation to the forward end of the piston 87 and provides a bearing for the piston rod 85. Rearward leakage of compressed air past the piston 87 is avoided 2,84 ameby an O-ring sealing member 95 seated within aperiphera1 groove 97in the piston.

In operation, when the trigger 68I'is depressed to open the valve 63, substantially unrestrainedmovementof the compressed air. through the passage .61 to the driving piston 35 occurs while simultaneously compressed air bleeds through the restricted duct 92 to the forward: end of the sear control piston 87 until predetermined pressure to overcome the biasing spring 88 thrusts against the piston'87 to drive-thepistonlrearwardly and thus-rock the lever 81 and thereby the-sear 75 to driver releasing position. The correlation is such that the momentary lag in the fluid pressure release of :the sear 75' assures fullnfluidpressure developmenton the head of the piston 35,.so that whenithesear releases the forming and driving mechanism fires under fullupressure'load tosever and drive the staple 18 and form the next succeeding staple blank. Insteadof. gradual acceleration'of the piston to the end of the driving stroke,aas in conventional practice, the piston operates'under full acceleration from the instant of release and instead of endingithe driving stroke with a jarring recoil, the driving stroke terminates with a cushioned-decelerated recoilless? stop. This cushioning results from a plurality of factors including compression loading of the spring 49; slight reduction in' drivingforce of the compressed air due to rapid expansion in the progressively increasing volumetric dis placement ibehind'the piston 35 during driving'stroke, and engagement of the skirt flange 50 of the piston with. the cushioning bumper 51.

It will be appreciated, of course, that the driving actioninitiated by pressing of the trigger 68 will occur so rapidly, even with the slight differential lagof the sear release, that to the operator the driving action will-seem to be virtually instantaneous. Promptlyuponrelease of the trigger 68, the valve 63, under theinfluence 'of' the biasing spring 71, closes the port 72, shutting off the pressure fluid supply, and the return spring 49 for the piston 35 returns the piston to initial position, while the spring 88 returns thesear operating piston '87 to its initial position, and the air driven back intothe delivery passage 61 by-there'turningpistonsexhausts from the passage through a spill-over passage 98-provided'by a slight clearance about the valve stem. 67 through the bushing 65. As the mechanism comes to rest, the sear snaps into retaining position behind the shoulder 79 of the forming and driving mechanism.

The sear actuatinglever 81 is also utilized for'feeding the staple blank strip by staple blank increments forwardly. For this purpose the lower end portion of the lever 81 is provided with a short forwardly directed arm 99 to which is pivotally attached a feeding lever or dog 100 engageable at its forward end in each rocking cycle of the lever 81 behind theshoulder'of theneXt succeeding formed. staple to move the strip by one staple blank incrementforwardly as the driver is retracted. A spring 101 biases the feed dog 100 normally counterclockwise as viewed in Figure 3 so as to retain the feed tip of the dog normally in engagement with the anvil 23. Limit upon' the retracting movement ofzthe: feed dog 100 is accomplished by limiting the retracting movement of the piston 87 as by means of a limit pin 102' operatively engaging within a longitudinal peripheral groove 103 inthe piston.

To retain the staple strip 19'against being dragged in reverse'during retraction of the feed dog 100, a pivotally mounted holding lever or dog 164 lSrPl'OVldfid below the feed dog and is normally biased at itsholding tip against the anvil 23 by means of a biasing-spring 105.

When a supply of staple blanks has been exhausted, a new roll of staple blanks can be inserted in themagazine' 15 by opening a'closure gate 107 which is normally held closed 'by latching mechanism 108. The end portion of the strip 19 from the newly insertedrollcan be quickly fedthrough the track provided by the plate 22 and over the top ofthe: anvil-.23 into engagement with the resiliently biasedretaininglever 104 so that in one preliminaryor nonproductivestroke of the-driving and forming mechanism 30, the. foremost staple-blank in-the-strip 19 will be formed and then fed forwardly into. the driveway 24- so that in each succeeding driving stroke of the-driver 33 a staple will be driven until all of the blanks in the strip 19 have been used successively.

In the modification of Figure 8 is shown'an adaptation of the inventionxto a stapling-machine 1-10 of atype utilizing preformed staples suppliedin stick form. Since'the only substantial difference in this machine as compared with the stapling machine 10 resides in the driving and sear mechanism, the fragmentary disclosure of Figure 8 will suffice to understand the construction, and it will be understood that the remainder of the machine and'its operation are substantially the same as described in connection with the machine 10, except as modified by'the description hereinafter.

The pneumatic stapling machine 110 has a body 111' whichmay be a-castingor molding, including a bottom or base structure 112 and ahead structure 113. The head structure 113 is vertically bored and carries a hardened generally cup-shapedcylinder 114 appropriately fixedly secured in place and provided with acentral downwardly opening driver blade passage 115 through which a vertically reciprocable driver blade 117 is operable under the driving impulsion of a pneumatically driven piston which may be in all essential respects like the piston 35 of the stapler 10 and similarly pneumatically actuated, and returned from a pneumatically motivated driving-stroke by coiled compression return spring 118. A rubber bumper 119 is provided in the bottom of the cylinder 114- as a stop atthe end ofthe driving stroke;

Vertically in line under the driver passage 115 is a staple guideway or driveway 120 into which successive staples 121 are fed from a staple-magazine 122 under forward pressure by a spring urged pusher 123. The staple driveway '1 2'0is provided by adownward nose projection 124 on tl:ie'body anda removable front nose piece 125 cooperativelyrelated and withthe-nose piece attached to the body of the machine by suitable means such as screws or the like (not shown).

For attaining full pneumatic driving pressure upon the driving piston, a driver delay or lag structure is provided comprising a sear member '127 which-is reciprocably slidably supported on a ledge 12'8 extending normal to the guid'eway'120 in spaced relation under the cylinder 114 but above the staple magazine-122. The sear member 127 has a forward upwardly facing shoulder 129 which is normally engageable in restraining relation with a lower end portion of the driver 117 and preferably with the tip of the driver.

The scar member 1'27'ha's a rearwardly directed stem 130 connected to a piston 131' which is slidably reciprocable in a cylinder 132 and is normally urged forwardly into driver restraining position by a coiled compression spr1ng'133 of predetermined-load characteristics thrusting at its forward end against the piston 131 and at its rear end resting against a bottoming disk or plate 134 at the inner end of the cylinder 132.

Retraction of the sear 127 is effected pneumatically by air pressure fed from the driver motivating feed passage through a restricted pressure bleed duct 135 communicating with a delivery port 137 in the cylinder 132 forwardly of the piston 131 and leading-into a pressure chamber defined between'the piston 1 31 and a closureplug 138 at the forward endportion of the cylinder and providing a bearing for'the sear shaft or stem'130.

When the air valve in control of the pressure fluid is opened, driving .of .the driver blade 117 is momentarilydelayed until :there is predetermined pressure-buildupas controlled by the sear 127 which is retracted only after predeterminedupressure has developed on the forwardsend of the piston 131-to overcome the biasing. load imposed by the spring 133. Thereupon, the sear 127 is snapped back out of blocking relation to the driver 117 and the pneumatic pressure on the driver piston impels the driver 117 down the staple driveway 120 with shot-like velocity, but smoothly cushioned at the end of the driving stroke to avoid jarring recoil of the machine. It will be observed that immediately above the sear the bottom of the cylinder 114 is provided with a downwardly projecting backup lip or flange 139.

Rearward or retraction movement of the piston 131 is limited by a stop pin 140 extending into a longitudinal limit defining groove 141 in the periphery of the piston. Upon release of the retracting pressure fluid force, the spring 133 drives the piston 131 and thereby the sear 127 forwardly against the back of the driver blade 117 and after the driver has been fully retracted by the return spring 118, the sear shoulder 129 snaps back into driver restraining position under the tip of the driver blade.

It will be observed that in both of the stapling machines It} and lift the cross-sectional area of the driver cylinders and the sear motivating piston cylinders is in substantial differential relation with the sear piston cylinders substantially smaller to a predetermined extent than the driver cylinders. In addition, of course, there is a reduction in the sear motivating piston area exposed to retracting pressure fluid to the extent of the displacement of the sear actuating stem or rod. This taken together with the loading of the sear biasing spring and the restricted fluid bleed delivery passage to the sear piston affords full assurance of complete fluid pressure buildup on the pressure end of the driver piston before the sear is released from the driver. Positive, substantially recoil free operation of the machine is thus assured.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. In combination in a portable pneumatic driving machine, a body structure including a handle portion connected to a base portion and a head portion, said head portion having a cylinder and a piston in the cylinder adapted to be connected to a driver, a sear member reciprocably mounted in said head portion for retaining engagement with the driver, a piston and cylinder carried by said base structure and connected to the sear, a spring normally biasing the piston to drive the same for urging the sear into driver restraining position, an air supply header in said handle, an air supply passage in said handle in ported communication with said header, a normally closed valve controlling movement of compressed air from the header to said delivery passage, said delivery passage communicating with said driver piston for urging the same in driver motivating direction and communieating with said sear piston to urge the same in opposition to said spring, said valve having a motivating stem projecting therefrom and exposed adjacent the forward portion of the handle, and a trigger mounted on said body and operable to act upon said stem to open the valve when the trigger is actuated to admit air into said delivery passage from the header for motivating the pistons in coordinated relation.

2. In a fastener driving machine, a body structure, said body structure having a base and a forward end portion, said forward end portion having a fastener driver reciprocal vertically therein, a pneumatic piston for motivating said driver in a driving stroke, means for supplying fasteners into position for driving by said driver, a pneumatic system in the upper portion of said body for actuating said piston, a valve for controlling said pneumatic system having a lever manually operable to actuate the valve, a sear for normally restraining the driver against movement in a driving stroke, a piston operated sear actuator mounted in said base structure and normally biased to maintain the sear in restraining relation to the driver, means for connecting 8- 1 said piston with the pneumatic system for operation following opening of said valve by said lever, and fastener feeding mechanism motivated by said sear actuator responsive to operations of the sear actuator piston.

3. In a fastener driving machine, a body structure, a driving member carried by the body structure, means carried by the body structure for supplying fasteners to be driven by said driving member, pneumatic driving means for said driving member, a sear structure for normally holding the driving member inactive and including a movable element carried by the body structure, said movable element being connected to a pneumatic piston, means for pneumatically operating said piston to move said element for releasing said sear, and a feed member carried by said element and operable in the movements of said element for feeding fasteners from said supply means.

4. In a machine for driving fasteners, a body structure, a pneumatically operable fastener driver reciprocably supported by the body structure, a pneumatic system carried by the body structure for supplying compressed air to drive said driver in a driving stroke, means carried by the body structure for controlling operation of the pneumatic system, the driver having a sear-engageable shoulder facing generally in the direction of driving movement of the driver, sear mechanism supported by the body structure and having a sear engageable with said shoulder for normally restraining the driver against movement in a driving stroke and including an operating member reciprocably carried by said body structure to move in a path away from the path of movement of the driver to release the sear from said shoulder without any com ponent of back thrust on said shoulder incident to said release, and means on the body structure leading from said pneumatic system and operative in response to operation of said control means for moving said sear-operating member in its path of movement away from the path of the driver to withdraw the sear and release the driver for a driving stroke in time lag relation and incident to development of a full pneumatic driving head for actuating the driver.

5. In a fluid pressure operated driving machine, a supporting unit including a head portion and a handle portion disposed rearwardly of the head portion for manipulating the unit, a driver having fluid operated means mounted within the head portion, a motivating pressure fluid system in said unit for said fluid operated means and including a digitally operable member movably mounted on said unit rearwardly of said head adjacent to the forward end of said handle portion for selective operation to control the pressure fluid system for motivating said pressure fluid operated means and thereby said driver, sear mechanism mounted in the rear part of the head portion and including a soar member having restraining interengagement with the driver and means for reciprocably guiding the sear member in a fore and aft relation below said digitally operable member with biasing means normally thrusting the sear member forwardly into restraining engagement with the driver, and means providing a connection between the motivating pressure fluid system and the sear mechanism and operable incident to control of the pressure fluid system as aforesaid by operation of the digitally operable member but in time lag relation thereto and after pressure fluid has been admitted to said pressure fluid operated means, whereby to release the sear member from the driver in opposition to said biasing means after the pressure fluid system is fully conditioned to effect full force driving of the fluid operated means and driver.

6. In a pneumatically operated driving machine, a supporting structure, a cylinder on said supporting structure having an upper end and a lower end, a piston supported for reciprocal driving and return stroke movements in said cylinder and having means projecting therebelow including a driver that extends beyond the lower end of the cylinder, means in the cylinder between the lower side of the piston and the lower end of the cylinder normally biasingly acting on the underside of the piston in concentrically balanced relation to project the piston and thereby the driver into a fully retracted position, means for supplying pressure fluid into the cylinder above the piston for driving the piston in a driving stroke away from said retracted position, and means carried by the supporting structure for restraining the piston and projecting means and driver as a unit against movement from said retracted position until a full predetermined pneumatic fluid head has developed in the cylinder over the piston so as to compel the piston to start from said retracted position under full acceleration of said predetermined pressure head, said biasing means acting between the piston and the lower end of the cylinder as the fluid pressure head diminishes in force toward the limit of the driving stroke to bring the piston and the driver to a cushioned decelerated recoiless stop, whereby to effect the driving stroke without terminal jarring recoil.

References Cited in the file of this patent UNITED STATES PATENTS 302,092 Bokenkotter July 15, 1884 1,568,260 Bates Jan. 5, 1926 1,761,640 Palmgren June 3, 1930 1,939,632 Randall Dec. 12, 1933 2,139,185 Engel Dec. 6, 1938 2,241,184 Clark May 6, 1941 2,482,993 Walker Sept. 27, 1949 2,535,588 Mead Dec. 26, 1950 2,567,390 Mead Sept. 11, 1951 2,585,940 Iuilfs Feb. 19, 1952 2,585,941 Iuilfs Feb. 19, 1952 2,698,938 Stebbings Jan. 11, 1955 

